The present invention relates to a long fiber-reinforced polypropylene resin composition for a molded article which is improved in all of a mechanical strength, a rigidity and an impact resistance as compared with those of conventional ones and which is excellent as well in a durability.
A so-called long fiber-reinforced polypropylene resin composition obtained by impregnating a molten polypropylene resin on a continuous fiber bundle for reinforcement and then carrying out a pulltrusion, followed by cutting it to a pellet having a length of 2 to 50 mm provides a molded article which is excellent in a mechanical strength, a rigidity and an impact resistance and therefore is widely used for uses in car parts, industrial parts and the like. However, the existing state is that all of these items are still unsatisfactory depending on uses and desired to be further improved.
A composition obtained by impregnating a modified polyolefin blended with an alkaline earth metal compound on a reinforced fiber bundle and then cutting it to a pellet was filed in International Publication WO99/20446 as international application for patent by the present applicants as a long fiber-reinforced polyolefin resin composition for a molded article which is improved in a mechanical strength and an impact resistance. This composition is satisfactory in a mechanical strength and an Izod impact strength but still unsatisfactory in a punching impact resistance and a durability.
Further, compositions prepared by blending long fiber-reinforced polypropylene polymer pellets with propylene-ethylene block copolymers are proposed as a glass fiber-reinforced polyolefin resin composition which is improved in a mechanical strength and an impact resistance (Japanese Patent Application Laid-Open No. 239286/1993 and Japanese Patent Application Laid-Open No. 173329/1995). These compositions are improved as well in a mechanical strength and an Izod impact strength but still unsatisfactory in a rigidity, a punching impact resistance and a durability.
As described above, a long fiber-reinforced polypropylene resin composition for a molded article which is improved in all of a mechanical strength, a rigidity, an impact resistance and specifically a punching impact resistance to a large extent and which is excellent as well in a durability has not yet been known, and such composition has been desired.
An object of the present invention is to solve the problems described above and to provide a long fiber-reinforced polypropylene resin composition which is more improved in all of a mechanical strength, a rigidity and an impact resistance than those of conventional ones and is excellent as well in a durability and which can suitably be used for wide applications.
Intensive investigations repeated by the present inventors in order to obtain a long fiber-reinforced polypropylene resin composition which can solve the problems described above. They have resulted in finding that very effective for solving the problems described above is a resin composition obtained by blending a long fiber-reinforced resin comprising as a base and a specific modified propylene polymer compounded with an alkaline earth metal compound with a specific crystalline propylene-ethylene copolymer as a diluent, and thus they have reached the present invention.
That is, the present invention comprises structures shown below.
The present invention relates to a long fiber-reinforced polypropylene resin composition comprising a long fiber-reinforced-propylene polymer composition (A) and a crystalline propylene-ethylene copolymer composition (B), wherein the former accounts for 55 to 90% by weight, and the latter accounts for 10 to 45% by weight.
The long fiber-reinforced propylene polymer composition (A) of the former comprises (A1), (A2) and (A3) shown below, and the blending proportions thereof are 20 to 64.9% by weight, 0.1 to 5% by weight and 35 to 75% by weight respectively;
(A1): a modified propylene polymer obtained by modifying a propylene homopolymer with an unsaturated carboxylic acid or an anhydride thereof, or a mixture of the above modified propylene polymer and an unmodified propylene homopolymer, wherein the isotactic pentad ratio (P value) is 96% or more, and the melt flow rate (230xc2x0 C., 21.18N; hereinafter abbreviated as ┌MFR┘) is 100 to 500 g/10 min,
(A2): at least one selected from the group consisting of simple substances, hydroxides and oxides of alkaline earth metals and
(A3): a long glass fiber having a length of 2 to 50 mm.
The crystalline propylene-ethylene copolymer composition (B) of the latter is a composition comprising (B1) and (B2) shown below in which the mixing proportion thereof is 0.001 to 1 part by weight of (B2) per 100 parts by weight of (B1);
(B1): 100 parts by weight of a crystalline propylene-ethylene copolymer having an MFR of 10 to 60 g/10 min comprising a propylene homopolymer part which is a polymer having an isotactic pentad ratio (P value) of 96% or more, a ratio (Q value) of a weight average molecular weight (Mw) to a number average molecular weight (Mn) being 6 or less and a hexane extract content of 0.8% by weight or less, and a propylene-ethylene copolymer part and
(B2): 0.01 to 1 part by weight of a nucleating agent.
The preferred embodiment of the present invention is the resin composition described above, wherein the modified propylene polymer or the mixture of the above modified propylene polymer and the unmodified propylene homopolymer (A1) has an MFR of 100 g/10 min or more and less than 300 g/10 min.
Another preferred embodiment of the present invention is the resin composition described above, wherein the propylene homopolymer part (B1) contained in the crystalline propylene-ethylene copolymer has an isotactic pentad ratio (P value) of 97% or more.
More preferred embodiment of the present invention is the resin composition described above, wherein the long fiber-reinforced propylene polymer composition (A) is a pellet produced by a melt-pulltrusion method.
Further preferred embodiment of the present invention is the resin composition described above, wherein the unsaturated carboxylic acid or anhydride thereof is maleic anhydride.
Further preferred embodiment of the present invention is the resin composition described above, wherein at least one selected from the group consisting of simple substances, hydroxides and oxides of alkaline earth metals is magnesium hydroxide.
The modified propylene polymer (A1) obtained by modifying a propylene homopolymer with unsaturated carboxylic acid or an anhydride thereof, or the mixture of the above modified propylene polymer and an unmodified propylene homopolymer constituting the long fiber-reinforced propylene polymer composition (A) according to the present invention has to have an isotactic pentad ratio (P value) of 96% or more and an MFR of 100 to 500 g/10 min, preferably 100 g/10 min or more and less than 300 g/10 min in terms of an improving effect for the rigidity, the impact resistance and the durability. Also when (A1) is the mixture of the modified propylene polymer and the unmodified propylene homopolymer, the mixture has to fall in the range described above. However, it is more preferred in terms of an improving effect for the rigidity, the impact resistance and the durability that the unmodified propylene homopolymer is not used and the substantially whole amount of (A1) is the modified propylene polymer.
In this case, the isotactic pentad ratio shows an isotactic ratio in terms of a pentad unit in a molecular chain and can be determined based on the descriptions of Macromolecules 8, 687 (1975) by means of 13C-NMR.
A production process for the modified propylene homopolymer described above includes a process in which 100 parts by weight of a propylene homopolymer having an isotactic pentad ratio of 96% or more is molten and kneaded with 0.1 to 5 parts by weight of an unsaturated carboxylic acid or a derivative thereof and 0.01 to 0.5 part by weight of an organic peroxide per 100 parts by weight of the above polymer. A blending amount of the organic peroxide has to be suitably controlled so that the MFR falls in the range described above.
A production process for the propylene homopolymer having an isotactic pentad ratio of 96% or more shall not specifically be restricted, and any of publicly known processes can be adopted. A process disclosed in Japanese Patent Application Laid-Open No. 104907/1983 can be given as one example thereof.
The unsaturated carboxylic acid or anhydride thereof described above includes acrylic acid, methacrylic acid, maleic acid, Nadic Acid (brand name: endo-cis-bicyclo-[2,2,1]hepto-5-ene-2,3-dicarboxylic acid), fumaric acid, itaconic acid, maleic anhydride, Nadic Anhydride (brand name: endo-cis-bicyclo-[2,2,1]hepto-5-ene-2,3-dicarboxylic anhydride) and itaconic anhydride, and maleic anhydride is preferred from a viewpoint of a reinforcing effect of a glass fiber.
To be specific, magnesium hydroxide, calcium hydroxide and magnesium oxide are given as the examples of the simple substances, hydroxides and oxides of alkaline earth metals (A2) of described above constituting the long fiber-reinforced polypropylene polymer composition (A) according to the present invention. They can be used alone or in combination of two or more kinds thereof. Magnesium hydroxide is preferably used because it is effective for improving the rigidity and the impact resistance.
A continuous glass fiber bundle is used as a raw material for the long glass fiber (A3) of described above having a length of 2 to 50 mm constituting the long fiber-reinforced polypropylene polymer composition (A) of the present invention, and this is commercially available as glass roving. Usually, it has an average fiber diameter of 4 to 30 xcexcm, a converged filament number of 400 to 10,000 filaments and a tex yarn number count of 300 to 20,000 g/km, and it has preferably an average fiber diameter of 9 to 23 xcexcm and a converged filament number of 1,000 to 6,000. From a viewpoint of a reinforcing effect, it is preferably subjected on a surface thereof to silane treatment for the sake of providing the resin with a surface adhesive property.
The blending proportions of (A1) to (A3) are 20 to 64.9% by weight of (A1), 0.1 to 5% by weight of (A2) and 35 to 75% by weight of (A3).
Any of processes publicly known as a melt-pulltrusion process can be employed as a production process for the long fiber-reinforced propylene polymer composition of (A). Usually, employed is a process in which a molten resin comprising (A1) and (A2) is fed from an extruder into an impregnating bath provided at a tip of the extruder. A continuous glass fiber bundle which is a raw material for (A3) is passed therethrough to impregnate the molten resin on the above glass fiber bundle and then pulled out through a nozzle and cut into a pellet having a length of 2 to 50 mm.
Capable of being used as a method for feeding (A1) and (A2) are;
1) a method in which the modified propylene polymer and the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) are dry-blended and put the blend into a hopper of an extruder,
2) a method in which the modified propylene polymer, the unmodified propylene homopolymer and the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) are dry-blended and put the blend into a hopper of an extruder,
3) a method in which the propylene homopolymer, the unsaturated carboxylic acid or anhydride thereof, the organic peroxide and the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) are dry-blended and put the blend into a hopper of an extruder where the modification is carried out at the same time, and
4) a method in which an extruder having at least two inlets for feeding materials is used and while putting thereinto a dry-blended mixture of the propylene homopolymer, the unsaturated carboxylic acid or anhydride thereof, and the organic peroxide from the first inlet for feeding to carry out the modification, the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) is put thereinto from the second inlet for feeding. The methods 1), 2) and 4) are preferred from a viewpoint of an effect for improving the rigidity, the impact resistance and the durability.
Any of publicly known methods can be employed as the impregnating method as long as they are methods in which a good impregnating property is obtained. For instance, a method can be employed in which a glass fiber bundle is brought into contact with a surface of a spreader and passed thereon while applying tension to thereby impregnate it with a molten resin (Japanese Patent Publication No. 37694/1988), and a method can be also employed in which a glass fiber bundle is passed between a pair of pins for opening fibers provided in an impregnating dice in a non-contact state to thereby impregnate it with a molten resin (International Publication WO97/19805). The latter is a preferred method because less produced are plumes in drawing at a high speed.
Similarly from a viewpoint of an effect for improving the rigidity, the impact resistance and the durability, the crystalline propylene-ethylene copolymer (B1) constituting the crystalline propylene-ethylene copolymer composition (B) according to the present invention has to be a copolymer having an MFR of 10 to 60 g/10 min comprising a propylene homopolymer part which has an isotactic pentad ratio (P value) of 96% or more, an Mw/Mn (Q value) of 6 or less and a hexane extract content of 0.8% by weight or less, and a propylene-ethylene copolymer part. The isotactic pentad ratio (P value) is preferably 97% or more. Further, a total ethylene content in the copolymer (B1) has to be less than 30% by weight. In this respect, the weight average molecular weight Mw and the number average molecular weight Mn can be determined respectively by means of GPC (gel permeation chromatography).
The production process for the copolymer described above shall not specifically be restricted, and any of publicly known processes can be employed. A process disclosed in Japanese Patent Application Laid-Open No. 269124/1996 can be given as one example thereof. That is, it is a process in which a highly stereospecific catalyst obtained from a solid catalyst component comprising a magnesium atom, a titanium atom, a halogen atom and a polyvalent carboxylic acid ester, an organic aluminum compound such as triethylaluminum, and an electron-donating compound such as t-butyltriethoxysilane is used to carry out homopolymerization of propylene as the first step, followed by the copolymerization of propylene with ethylene as the second step. The above copolymerization is carried out usually at a polymerization temperature of 20 to 80xc2x0 C. and under a pressure of 5 MPa or less. In this respect, a method for feeding propylene and ethylene to a polymerization vessel shall not specifically be restricted, but the content in a copolymerization part is preferably 30 to 80% by weight. The polymerization by a slurry method is preferred in order to allow the hexane extract content to fall in the range described above.
In respect to the copolymer composition (B) according to the present invention, 0.01 to 1 part by weight of the nucleating agent (B2) per 100 parts by weight of the copolymer (B1) described above is preferably blended from a viewpoint of an effect for improving the rigidity, the impact resistance and the durability. Capable of being recited as the examples of the nucleating agent are talc, succinic acid, lithium benzoate, sodium benzoate, aluminum hydroxy-bis(4-t-butylbenzoate), 1xe2x80xa23,2xe2x80xa24-dibenzylidene-sorbitol, 1xe2x80xa23,2xe2x80xa24-bis(p-methylbenzylidene)sorbitol, 1xe2x80xa23,2xe2x80xa24-bis(p-ethylbenzylidene)sorbitol, 1xe2x80xa23,2xe2x80xa24-bis(2xe2x80x2, -4xe2x80x2-dimethylbenzylidene)sorbitol, 1xe2x80xa23,2xe2x80xa24-bis(3xe2x80x2, 4xe2x80x2-dimethylbenzylidene)sorbitol, 1xe2x80xa23-p-chlorobenzylidene-2xe2x80xa24-p-methylbenzylidenesorbitol, sodium-bis(4-t-butylphenyl)phosphate, sodium-2,2xe2x80x2-methylene-bis(4,6-di-t-butylphenyl)phosphate, a mixture (1:1:1 (weight ratio)) comprising ternary components of aluminum dihydroxy-2,2xe2x80x2-methylene-bis(4,6-di-t-butylphenyl)phosphate, aluminum hydroxy-bis[2,2xe2x80x2-methylene-bis(4,6-di-t-butylphenyl)-phosphate] and lithium stearate, poly-3-methyl-1-butene, polyvinylcyclohexane, polyallyltrimethylsilane and N,Nxe2x80x2-dicyclohexyl-2,6-naphthalenedicarboxyamide.
The form of the above copolymer resin composition (B) shall not specifically be restricted and may be pellet, granular, flaky or powdery. A pellet obtained by mixing (B1) and (B2) then, melting and kneading the mixture is preferably used.
In the present invention, the long fiber-reinforced propylene polymer composition (A) can be blended with the crystalline propylene-ethylene copolymer composition (B) by a dry blending system. It is rather preferred to obtain a composition having an improved rigidity, impact resistance and durability that they are fed directly into a molding machine such as an injection-molding machine after dry-blending without passing through an extruder in order to maintain a length of the fibers included in the composition. The blending proportion thereof is determined depending on a glass fiber content in the long fiber-reinforced propylene polymer composition (A) and a glass fiber content required to the final molded article. It is preferably 55 to 90% by weight of (A) and 10 to 45% by weight of (B) from a viewpoint of improving the rigidity, the impact resistance and the durability.
In addition to those described above, an antioxidant, a light stabilizer, a UV absorber and an antistatic agent can be added, if necessary, to the composition of the present invention.
Publicly known molding methods such as an injection-molding method, an extrusion-molding method, a blow-molding method, a compression-molding method and an injection compression-molding method can be applied without any restrictions to a production method for a molding article obtained from the long fiber-reinforced polypropylene resin composition of the present invention. In particular, an injection-molding method, a compression-molding method and an injection compression-molding method are preferred. The resulting molded article can widely be used for various uses from small-sized to large-sized ones. Among them, it can suitably be used in uses for medium-sized to large-sized molded articles for automobiles.